You always need to read what the machine generated for you; the machine can only write code for you, not understand code for you. Here, the biggest issue is that copy might not work if the input and output containers are different, if the input has multiple framerates or audio tracks, etc.

Well done. I recently revived the BadRAM kernel patch in order to do something similar; memtest86+ supports that functionality too, using <F4>, <F4>, <F10>, <F10>.